This invention relates to a method of blanching vegetable material and in particular to a method of blanching vegetable material prior to freezing.
Most vegetables require a short heat treatment or blanching to inactivate enzymes and kill bacteria. The blanching stabilises the quality of the vegetables prior to and during frozen storage.
Several types of blanching methods are known. Vegetables may be blanched in hot water, e.g. by transferring the vegetables from a container with cold washing water to successive containers containing water of increasing temperatures, e.g. up to 98° C., and finally to a container with cold water for cooling it down again. Alternatively, the vegetables may be passed on a belt through a bath of hot water, e.g. at 98° C., and then into cold water. Blanching methods using steam are also known. The vegetables may be conveyed on a belt with steam jets directed from the top and bottom to cause rapid heating. The vegetables are then cooled in cold water. In some instances cold water sprays are used instead of immersion cooling in cold water in order to prevent excessive leaching of nutrients. Ambient air may also be used to cool vegetables by drawing air through the vegetables causing convection cooling and evaporative cooling.
EP-A-498972 discloses a blanching or part-cooking process in which the vegetable material is contacted with saturated steam while it is supported on a moving conveyor and while it is not submerged in a liquid and exposing the vegetable material at least during part of this treatment with microwave radiation. In one embodiment the heat treated vegetable material is subsequently cooled down by contacting it with finely divided water (liquid or solid) having a temperature not exceeding 5° C. and preferably having a temperature between 0° C. and −10° C. It is stated that the vegetables have a better texture and taste compared with those treated with steam or hot water and cooled in running water.
It is an object of the present invention to provide an alternative blanching method.